Darwin's Island Read Free Page B

sapiens shares its nature with other primates. The book uses our own species as an exemplar of evolution.
    To the founder of modern biology, man obeyed the same evolutionary rules as all his kin and shared much of his physical being with them; as the book says, in its final paragraph, he still bears ‘the indelible stamp of his lowly origin’. In moral terms Homo sapiens was something more: ‘. . . of all the differences between man and the lower animals, the moral sense or conscience is by far the most important. This sense . . . is summed up in that short but imperious word “ought,” so full of high significance. It is the most noble of all the attributes of man, leading him without a moment’s hesitation to risk his life for that of a fellow-creature.’ No ape understands the meaning of ‘ought’, a word pregnant with notions quite alien to every species apart from one. Even so, despite that essential and uniquely human attribute, every ape - and we are among them - is, like every other creature, the product of a common biological mechanism.
    The logic of evolution is simple. There exists, within all plants and animals, variation passed from one generation to the next. More individuals are born than can live or breed. As a result, there develops a struggle to stay alive and to find a mate. In that battle, those who bear certain variants prevail over others less well endowed. Such inherited differences in the ability to transmit genes - natural selection, as Darwin called it - mean that the advantageous forms become more common as the generations succeed each other. In time, as new versions accumulate, a lineage may change so much that it can no longer exchange genes with those that were once its kin. A new species is born.
    Natural selection is a factory that makes almost impossible things. It manufactures what seems like design with no need for a designer. Evolution builds complicated organs like the eye, the ear or the elbow by piecing together favoured variants as they arise. Almost as an afterthought, it generates new forms of life.
    Its tale as told in The Origin of Species turns on the efforts of farmers as they develop new breeds from old, on changes in wild creatures exposed to the rigours of nature and the demands of the opposite sex, on the tendency of isolated places to evolve unique forms, and on the silent words of the fossils that tell of a planet as it was before evolution moved on. Its pages speak of the embryo as a key to the past and of how structures no longer of value and others that appear almost too perfect are each testimony of the power of natural selection. The geography of life, on islands, continents and mountains, is also evidence of the common descent of mushrooms, mice and men. Most of all, life’s diversity can be arranged into a series of groups arranged within groups, of ever-decreasing affinity, as a strong hint that they split apart from each other longer and longer ago.
    The Descent of Man uses that logic to disentangle the history of a single species. Unique as it might think itself, Homo sapiens is animal like all others. The book’s famous last sentence reads, in full: ‘I have given the evidence to the best of my ability: and we must acknowledge, as it seems to me, that man with all his noble qualities, with sympathy which feels for the most debased, with benevolence which extends not only to other men but to the humblest living creature, with his god-like intellect which has penetrated into the movements and constitution of the solar system - with all these exalted powers - Man still bears in his bodily frame the indelible stamp of his lowly origin.’
     
    In 1871 - and even in 1971 - the evidence for that final and provocative statement was weak indeed. Now, everything has changed. The entire evolutionary case can be made in terms of ourselves and our relatives; of apes and monkeys, of chimps and gorillas, and of men and women. Our new ability to look at genes, cells,